In a general turbine (for example, steam turbine), a rotor as a rotating shaft is rotatably supported by a casing, rotor blades are installed on the outer circumferential portion of the rotor, stator vanes are disposed on the inner wall of the casing, and a plurality of the rotor blades and a plurality of the stator vanes are alternately disposed in a steam passage. In a process in which steam flows through the steam passage, the rotor blades and the rotor are driven to rotate.
The rotor blade includes a blade root portion fixed to a rotor disk of the rotor, a platform formed integrally with the blade root portion, and a blade portion which has a base end portion joined to the platform and extends toward the tip end portion. In addition, the base end portions of the plurality of rotor blades are fixed to the outer circumferential portion of the rotor disk so as to be arranged along the circumferential direction thereof.
For example, the rotor blades of the steam turbine rotate on a path on which steam flows. At this time, steam in the vicinity of the final stage of a low-pressure steam turbine contains a large amount of fine droplets. Therefore, due to the impacts of the water droplets at high speeds, the leading edge portion of the blade tip end in the rotor blade may be eroded and reduced in thickness.
As measures against erosion, for example, as described in Patent Literatures 1 and 2, there is a method for forming an erosion shield at the leading edge portion of the tip end of a rotor blade. In Patent Literature 1, an erosion shield is formed by cladding by welding through plasma transferred arc welding. In Patent Literature 2, it is described that powder of a hard material is melted through high-density energy irradiation (a laser or electron beam) and is subjected to cladding by welding to form a hard layer, and a portion of a member is locally replaced with the hard layer such that an erosion preventive portion (erosion shield) is provided.